Apparatus and process for stretch breaking filamentary tow



Sept. 30, 1969 D. L. GARRISON ET AL APPARATUS AND PROCESS FOR STRETCH BREAKING FILAMEN'IARY TOW Filed 001:. 23, 1967 INVENTORS DALE L. GARRISON ARTHUR LULAY BY W AGENT United States Patent 3,469,285 APPARATUS AND PROCESS FOR STRETCH BREAKING FILAMENTARY TOW Dale Leroy Garrison, Newark, and Arthur Lulay, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Oct. 23, 1967, Ser. No. 677,107 Int. Cl. D01g 1/08 US. Cl. 19-.37 3 Claims ABSTRACT OF THE DISCLOSURE An improvement is provided in means for stretch breaking a moving continuous synthetic filament tow to staple fiber sliver. Prior art means comprises differentially driven feed and forwarding means with breaker means in the zone between them. The improvement comprises snubbing means between the feed and breaker means to apply additional tension to the filaments before they are broken. An improved method providing for passing of the fiber sheet is contact with at least one guide to change. the angle of movement of the fiber sheet is disclosed.

A preferred ratch setting and the utilization of rebreaker means are also disclosed.

The improvements result in a reduction in the incidence of fibers shorter than the average desired length.

This invention relates to an improvement in the art of stretch breaking a tow of synthetic filaments to provide a sliver of staple fibers from which staple yarns can be made by conventional methods. More particularly, the invention relates to stretch breaking a synthetic tow to provide a sliver having a very low level of short fibers.

BACKGROUND OF THE INVENTION In the production of staple yarns, one widely used conventional method comprises passing a tow sheet of continuous synthetic filaments between a pair of upper and lower feed nip rolls and a pair of upper and lower delivery nip rolls operated at a higher peripheral speed than the feed nip rolls, with a breaker means positioned between the pairs of rolls for increasing the tension upon the filaments in the tow sheet and inflicting stress concentration points upon the filaments to break them progressively to staple fiber length without destroying the continuity of the resulting sliver. The sliver so produced is then processed to conventional staple yarns by known methods. Apparatus suitable for carrying out the stretchbreaking process is described by Lohrke in his US. Patent 2,419,320 and by Wyatt in his US. Patent 2,748,- 426. Commercial apparatus for carrying out the stretchbreaking process customarily includes means for predrawing the tow sheet and crimping the resulting sliver, if desired.

Although the stretch-breaking process for conversion of tow sheets to staple sliver is widely used because it is economical, the apparatus available hitherto for producing the economical, the apparatus available hitherto for producing the sliver results in the production of a sliver containing numerous short fibers. The incidence of fibers shorten than the average desired length causes such problems as thin spots in the sliver, neps in the staple yarn product, and fly and waste resulting from short fibers becoming detached from the sliver during its processing to staple yarns. The problem of short fibers is particularly severe with synthetic filaments having a high break elongation. The problem is also very severe when the distance between the breaker means and delivery nip 'ice rolls is set at about 10 inches (about 25 cm.) or more in an effort to produce a sliver composed of staple fibers of high average length, since the short fibers which are formed make it ditficult to increase the average staple fiber length significantly.

OBJECTS OF THE INVENTION Accordingly, an object of the present invention is to provide improved apparatus and process for stretch breaking a tow of synthetic filaments to produce a sliver of staple fibers with minimum formation of short fibers.

SUMMARY OF THE INVENTION In accordance with the present invention, an improvement is provided in means for stretch breaking a moving tow of continuous synthetic filaments to a continuous sliver of staple fibers which comprises feed means for forwarding a fiber sheet in the form of a tow of continuous filaments, delivery means in spaced relation with the feed means for receiving the fiber sheet in the form of a continuous sliver of staple fibers and forwarding the fiber sheet at a higher speed than the feed means, and breaker means positioned in the interval between the feed means and the delivery means for tensioning the filaments and inflicting stress concentration points upon the filaments. The improvement comprises snubbing means in the interval between the feed and breaker means to apply additional tension to said continuous filament before they are broken by said breaker means. The snubbing of the fiber sheet is preferably effected by passing it in contact with at least one guide between the feed means and the breaker means to change the angle of movement of the fiber sheet as it passes between the feed means and the breaker means thereby applying additional tension to the continuous filaments before they are broken by the breaker means.

PREFERRED EMBODIMENTS In a preferred embodiment of the invention, the snubbing means is at least one guide and most preferably two or more guides. The guide(s) is preferably a non-rotatable cylindrical pin; however, other elements such as frictional control bars, surface driven pins, or rolls are also suitable. It is necessary that the snubbing means apply force to the moving fiber sheet to apply additional tension to said continuous filaments before they are broken by the breaker means. When a non-rotatable guide (e.g., cylindrical pin) is used, the guide is positioned to change the angle of movements of the fiber sheet as it passes between the feed means and the breaker means. This insures adequate contact between the guide and the fiber sheet to impart a suflicient frictional force to the fiber sheet and thereby increase the tension upon it. When two or more of these guides are used, this angle of movement or travel is changed at least twice. When other types of snubbing means are used (e.g., surface driven rolls), a change in the angle of movement of the fiber sheet may be unnecessary; sufiicient snubbing may be effected by the spacing of the surface driven rolls, etc.

In a highly preferred embodiment, the distance between the nip of the breaker means and the nip of the delivery means is at least about 10 inches (at least about 25 cm.). This setting provides a high average fiber length with a significant reduction in the incidence of short fibers.

In another highly preferred embodiment, a rebreaker means comprising at least one pair of upper and lower rebreaker nip rolls for receiving the fiber sheet from the delivery means and forwarding the fiber sheet at a higher speed than the delivery means is provided. This distance between the nip of the delivery means and the nip of the rebreaker means is preferably less than the distance between the nip of the breaker means and the nip of the delivery means.

The specific apparatus preferably being improved upon comprises pair of differentially driven upper and lower horizontal axis fed and delivery nip rolls in spaced relation and a cooperative pair of upper and lower rotary horizontal axis breaker rolls in the interval between the feed and delivery rolls.

DRAWING The invention will be better understood by reference to the attached figures, in which preferred embodiments of the invention are illustrated.

FIGURE 1 is a schematic drawing illustrating the breaking and drafting section of a stretch-breaking machine incorporating snubbing means in accordance with the present invention; and

FIGURE 2 is a schematic drawing illustrating the breaking and drafting section of a stretch-breaking machine incorporating snubbing means and further modified by inclusion of rebreaking means.

Referring now to FIGURE 1, fiber sheet 1 comprises a tow sheet of synthetic continuous filaments, which if desired may have been heated and drawn in a preceding section (not shown) of the stretch-breaking machine in accordance with known procedure. The fiber sheet is received and fed at a given desired speed by feed means 2 to delivery means 3, which receive and forward the fiber sheet at a higher speed than the feed means. In accordance with the present invention, after the fiber sheet issues from the feed means, it is pretensioned by snubbing means 4 and the continuous filaments in the fiber sheet are then broken to staple fibers by breaker means 7. Feed means 2 comprises a pair of upper and lower feed nip rolls 5 and 6, which may correspond with rolls 5 and 6 of FIGURE 4 of US. Patent 2,748,426 to W. K. Wyatt; and delivery means 3 comprises a pair of upper and lower delivery nip rolls 9 and 10, which may correspond with rolls 9 and 10 of FIGURE 4 of the same patent. Snubbing means 4 comprises non-rotatable, cylindrical pins 11 and 12 positioned such that the moving fiber sheet, passing over one pin and under the other, is forced to change the direction of its linear movement twice before passing into the breaker means. The breaker means 7 comprises a pair of upper and lower intermeshing rotatable members 13 and 14 carrying radially affixed blades 15. The blades 15 may be of various shapes and materials of construction, but commonly are rectangular bars of silicon carbide or a hard ceramic material. Intermediate guide 8, which may correspond with the guide shown in FIGURE 15 of US. 2,748,426 and shown more schematically as element 151 in FIGURE 4 of the same patent, regulates the width of the fiber sheet. As the fiber sheet leaves the delivery roll, now in the form of a continuous sliver of staple fibers, it is directed upwardly to pass over the top edge of the vertically arranged plate 16 to the collection means (not shown) after being subjected to crimping or any other desired intermediate steps.

The distance from the snubbing means to the nip of the breaker means may be as little as 1 inch or even less, or it may be as high as about 10 inches. The point in the snubbing means from which this distance is measured is the point from which the fiber sheet departs from the snubbing means. The nip of the breaker means is measured from the first point of contact of the breaker bars on the fiber sheet when measuring on the feed means side; or from the last point of contact of the breaker bars on the fiber sheet when measuring on the delivery means side.

The nominal maximum staple length of the staple fibers in the continuous sliver prepared on the stretch-breaking machine of the present invention is equal to the ratch setting (the distance between the nip of the breaker bars and the nip of the rolls in the delivery means). However, the staple fiber lengths actually observed fall into a spectrum, or fiber diagram, ranging downward to extremely short fibers. The optimum spectrum of staple fiber lengths, or 45 fiber diagram, is usually considered to be a uniform distribution of fiber lengths ranging from the ratch setting as the maximum to about 2 inches (about 5 cm.) as a minimum.The modified stretch-breaking apparatus of the present invention is successful in greatly reducing the incidence of short staple fibers as compared with the same apparatus in which the snubbing pins are removed. Although the results vary somewhat in accordance with the nature of the filaments being broken and the ratch setting, reductions of 50% and even 75% in the incidence of short fibers have been observed.

A tendency for the fiber diagram to be somewhat deficient in staple fibers having a length intermediate between the average fiber length and the ratch setting is frequently observed in practice. To remedy this deficiency and make fiber diagram more closely approach the optimum 45 fiber diagram, the continuous sliver may be rebroken. This operation consists of passing the continuous sliver between nip rolls spaced more closely together than the ratch setting, which breaks the longest fibers in the sliver again while permitting fibers shorter than the distance between nip rolls in the rebreaking operation to pass through without being broken again. In a highly preferred embodiment in the present invention, shown in FIGURE 2, the fiber sheet is passed from the delivery means to rebreaker means 17 comprising a pair of upper and lower rebreaker nip rolls 18 and 19, after which the fiber sheet in the form of the rebroken continuous sliver of staple fibers is passed over the plate 16 to the collection means (not shown) after being subjected to crimping or any other desired intermediate steps.

The following examples are intended to illustrate, without being limitative, the results which may be achieved by employing preferred embodiments of the improved stretch-breaking apparatus and process of the present invention.

Example I A commercially available stretch-breaking machine of the type shown in US. Patent 2,748,426 to W. K. Wyatt (manufactured by the Turbo Machine Company and designated as the Turbo Stapler) is modified as shown in FIGURE 1 by incorporating a 4-inch (1.9 cm.) diameter cylindrical snubbing pin composed of stainless steel at a distance of 4% inches (12.1 cm.) from the nip of the feed rolls and a second pin of the same diameter and material on a center 2% inches (5.40 cm.) horizontally beyond and inch (1.59 cm.) vertically below the center of the first pin. The distance from the second pin to the pin "f the breaker bars is 2.0 inches (5.1 cm.).

A tow composed of approximately 78,300 filaments 0f 6-denier bicomponent acrylic fiber in which the components are a mixture of polymers, the first of which has a composition of 93.8 wt. percent acrylonitrile, 0.2 wt. percent sodium styrenesulfonate, and 6.0 wt. percent of methyl acrylate, and the second having a composition of 99.38 wt. percent acrylonitrile, 0.02 wt. percent sodium styrenesulfonate, and 0.60 wt. percent methyl acrylate, is converted to a sliver of staple fibers on the modified stretchbreaking machine. The filaments in the tow have a tenacity of 0.95 g.p.d., a break elongation of 60%, a residual shrinkage of 2%. The width of the fiber sheet is 7.0 inches (17.8 cm.). Before being broken, the tow is drawn 1.31 X at a heater plate temperature of 300 F. (149 C.). The speed of the fiber sheet is 14.7 y.p.m. (yards per minute) which is equal to 13.4 m.p.m. (meters per minute) at the feed nip rolls, and the speed of the fiber sheet at the de livery nip rolls is 55.0 y.p.m. (50.3 m.p.m.), with a corresponding break zone draft of 3.74 The breaker bar draft (ratio of surface speed of delivery rolls to that of the breaker bars) is 1.37 The ratch setting is 8.0 inches (20.3 cm.). The breaker bars are rectangular bars of a hard ceramic material composed of alumina, silica, and magnesia (sold as AlSiMag 512 by the American Lava Co.)

having a width of 0.14 inch (0.36 cm.) and set at a depth of /32-11101'1 (0.86 cm.) The condensing draft (ratio of crirnper roll speed to delivery roll speed) is 1.00. The average length of the staple fibers in the continuous sliver so produced (designated as the test sliver) is 6.34 inches (16.10 cm.), and the sliver contains only 9% of fibers shorter than 2.0 inches (5.1 cm.). In a control run in which the snubbing pins are removed, the length of the staple fibers is only 3.68 inches (9.35 cm.) and 35% of the fibers are shorter than 2.0 inches (5.1 cm.), by contrast. The test and control slivers are processed to worsted count staple yarns in conventional manner and under identical processing conditions. The evenness properties of the resulting yarns are given in the following table:

Test yarn Control yarn 1 Coefiicient of variance.

Example II This example illustrates the improvement in the stretchbreaking of tows at high ratch settings achieved in accordance with the present invention.

The modified stretch-breaking machine of Example I is employed for stretch-breaking a tow of approximately 157,000 filaments of 3-denier acrylic fiber composed of 93.8 wt. percent acrylonitrile, 6. wt. percent methyl acrylate, and 0.2 wt. percent sodium styrenesulfonate. The filaments in the tow have a tenacity of 2.3 g.p.d., a break elongation of 28%, and a residual shrinkage of 1.5%. The width of the fiber sheet is 7.0 inches (17.8 cm.). Before being broken, the tow is drawn 1.58X at a heater plate temperature of 280 F. (138 C.). The speed of the fiber sheet is 9.17 y.p.m. (8.38 m.p.m.) at the feed nip rolls, and the speed of the fiber sheet at the delivery nip rolls is 55.0 y.p.m. (50.3 m.p.m.), with a corresponding break zone draft of 6.00 The breaker bar draft is 137x, and the breaker bars are set at a depth of 0.50 inch (1.27 cm.). The ratch setting is 14.0 inches (35.6 cm.). The condensing draft is 1.03. The average length of the staple fibers in the continuous sliver so produced (designated as the test sliver) is 7.09 inches (18.0 cm.), as contrasted with only 5.11 inches (12.98 cm.) for the average length of the staple fibers in a control sliver produced by omitting the snubbing pins but otherwise using identical conditions. The percentage of short fibers produced in the test and control slivers are given in the following table:

Percent fibers having a length below Test sliver Control sliver 2.0 inches (5.1 cm.) 5 8 4.0 inches (10.2 cm.) 27 52 6.0 inches (15.2 cm.) 45 70 Example III diameter cylindrical snubbing pin composed of stainless steel is employed instead of two snubbing pins. The distance from the nip of the feed rolls to the snubbing pins. The distance from the nip of the feed rolls to the snubbing pin is 6 /8 inches (17.5 cm.), and the distance from the snubbing pin to the nip of the breaker means is 2.0 inches (5.1 cm.). The fiber sheet is passed over the snubbing pin, the top of which is inch (0.56 cm.) above a line connecting the nip of the feed means with the nip of the breaker means. The average length of the staple fibers in the continuous sliver so produced is 5.22 inches (13.26 cm.), and the sliver contains only 18% of fibers shorter than 2.0 inches (5.1 cm.).

As noted in Example I, a continuous sliver produced under essentially identical conditions except that no snubbing pin is employed has an average fiber length of only 3.68 inches (9.35 cm.), and 35% of the fibers are shorter than 2.0 inches (5.1 cm.).

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not to be limited by the specific illustrations except to the extent defined in the following claims.

What is claimed is: 1. In apparatus for stretch breaking moving tow of continuous synthetic filaments to continuous sliver of staple fibers which comprises:

pairs of differentially driven upper and lower horizontal axis feed and delivery nip rolls in spaced relation and a cooperative pair of upper and lower rotary horizontal axis breaker rolls in the interval between the feed and delivery rolls, said feed and delivery rolls and said breaker rolls defining a linear path of travel for the fiber sheet, the improvement which comprises:

snubbing means in the interval between said feed and breaker rolls to apply additional tension to said continuous filaments before they are broken by said breaker rolls, said snubbing means comprising two non-rotatable stationary guides, the first of said guides spacially positioned to contact said moving tow after passage thereof through said feed nip rolls and to divert the said moving tow from said linear path of travel and the second of said guides spacially positioned to contact the diverted moving tow and to cause the said moving tow to again follow the said linear path of travel in moving toward the breaker rolls.

2. Apparatus according to claim 1 wherein the distance between the nip of said breaker rolls and said nip of said delivery nip rolls is at least about 10 inches.

3. Apparatus according to claim 1 further comprising rebreaker roll means for receiving the fiber sheet from the said delivery nip rolls and forwarding the fiber sheet at a higher speed than said nip rolls to again break the longer fibers in the fiber sheet.

References Cited UNITED STATES PATENTS 2,419,320 4/1947 Lohrke 19-41 XR 2,830,327 4/1958 Wildbolz 194l XR 2,941,259 6/ 1960 Lohrke 1939 DORSEY NEWTON, Primary Examiner 

